线程顺序打印的几种方式

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 static CountDownLatch latch = new CountDownLatch(1);
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 public static void main(String[] args) throws InterruptedException {
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    Thread thread1 = new Thread(() -> {
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        System.out.println("A");
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        latch.countDown();
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    });
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    thread1.start();
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    latch.await();
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    latch = new CountDownLatch(1);
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    Thread thread2 = new Thread(() -> {
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        System.out.println("B");
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        latch.countDown();
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    });
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    thread2.start();
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    latch.await();
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    latch = new CountDownLatch(1);
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    Thread thread3 = new Thread(() -> {
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        System.out.println("C");
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        latch.countDown();
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    });
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    thread3.start();
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    latch.await();
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}

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static CyclicBarrier barrier = new CyclicBarrier(1);
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public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
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    Thread thread1 = new Thread(() -> {
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        System.out.println("A");
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    });
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    thread1.start();
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    barrier.await();
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    barrier.reset();
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    Thread thread2 = new Thread(() -> {
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        System.out.println("B");
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    });
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    thread2.start();
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    barrier.await();
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    barrier.reset();
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    Thread thread3 = new Thread(() -> {
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        System.out.println("C");
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    });
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    thread3.start();
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    barrier.await();
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}

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static Semaphore semaphore = new Semaphore(1);
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public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
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    semaphore.acquire();
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    Thread thread1 = new Thread(() -> {
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        System.out.println("A");
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        semaphore.release();
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    });
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    thread1.start();
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    semaphore.acquire();
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    Thread thread2 = new Thread(() -> {
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        System.out.println("B");
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        semaphore.release();
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    });
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    thread2.start();
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    semaphore.acquire();
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    Thread thread3 = new Thread(() -> {
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        System.out.println("C");
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        semaphore.release();
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    });
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    thread3.start();
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}

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public static void main(String[] args) {
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    ExecutorService executorService = Executors.newSingleThreadExecutor();
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    for (int i = 0; i < 3; i++) {
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        int finalI = i;
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        executorService.submit(() -> {
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            System.out.println((char)('A' + finalI));
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        });
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    }
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}